Sheet glass manufacturing requires three steps, melting of raw material, forming the melted glass into the proper shape which in this case is thin glass sheets (e.g., 3 mm thick or less), and finally shaping the thin glass sheets into a final shape which is satisfactory for the user of the glass sheets. The final shaping step includes separating near net shaped thin glass sheets from the glass ribbon, sizing the thin glass sheets through a cutting operation and edging the thin glass sheets to strengthen the thin glass sheets for handling operations. The discussion herein relates to the edging of the thin glass sheets.
Thin glass sheet edging is typically done today by utilizing a grinding wheel which has groove(s) formed therein. The formed groove(s) create a shape on the edge of the thin glass sheet that mirrors the groove. Unfortunately, there are several problems with using a grinding wheel to edge the thin glass sheets. A list of several of these problems follows:
1. Producing a consistent formed groove in the grinding wheel is becoming increasingly difficult due to the thinner glass sheets.
2. The grinding wheel's formed groove becomes misshapen with use causing an inconsistent edge shape in the glass sheet.
3. The surface area being used by the grinding wheel is limited to the formed groove which increases the cost due to the poor utilization of material.
4. The relatively small area of the grinding wheel which can come into contact with the edge of the glass sheet necessitates the use of coarser grain sizes which ultimately results in a poorer surface finish on the edge of the glass sheet.
5. The edge polishing process is unable to remove major flaws in the edge of the glass sheet which are generated during the cutting process and limits the strength of the edge of the glass sheet.
6. The lack of chip clearance between the glass sheet and the grinding wheel during the grinding process increases the potential for causing defects in the glass sheet due to the grinding wheel becoming clogged by chips (e.g., glass particles) from the glass sheet.
7. Particulates (e.g., chips, glass particles) can be imbedded within the grinding wheel's grooves which can limit the effectiveness of the grinding wheel.
8. Improvements to edge finish smoothness requires a multi-step process of grinding wheels each with a separate motor-spindle requirement that increases cost, process losses and are difficult to setup.
9. The edge of the glass sheet after grinding (polishing) is not smooth enough to prevent particle trapping, which could contribute significantly to an undesirable surface particle count due to late particle release.
10. The grinding wheel process requires a large amount of stock (80 um to 200 um) to remove the scoring defects in the glass sheet. This generates a large amount of particles which contaminate and adhere to the surfaces of the glass sheet and require an expensive washing process to clean the surfaces of the glass sheet.
As stated above the current process of edging a thin glass sheet using the grinding wheel has several drawbacks, specifically when it comes to edge strength or in another term the durability of the edged thin glass sheet as it relates to handling. Accordingly, there is a need for a new edging process that overcomes the aforementioned problems and other problems associated with edging thin glass sheets. This need and other needs are satisfied by the present invention.